MX misconfigurations aren’t exactly breaking news. They’re a common issue that users deal with on a daily basis. When your MX (Mail Exchange) records aren’t properly set up, it can create serious problems, not just in terms of email delivery, but also for the overall security of your domain.
According to data from 2IP.io, Google has the largest share of MX records, handling email services for 11.82% of domains. Other major players include Outlook, GoDaddy, and Namecheap.
And that’s precisely where many of the problems start. Some providers fail to supply their users with the correct MX records, or even when they do, users often struggle to configure them properly.
In this article, we’ll explain what MX misconfigurations are, what kind of risks they pose, how attackers can take advantage of them, how to detect them, and what you can do to avoid falling into this trap.
Table of Contents
What Is an MX Record and Why Does It Matter?
MX records are a key part of your domain’s ability to send and receive email. They’re a type of DNS record that tells mail servers which server is responsible for receiving emails sent to your domain. CloudFlare denotes that “The MX record indicates how email messages should be routed in accordance with the Simple Mail Transfer Protocol.“
If you don’t have an MX record, the sending servers won’t know where to deliver the email; it’s like knowing someone’s name but having no address to send a letter to.
Every MX record includes a destination server and a priority level. That priority tells the sending server which destination to try first. If the first one is unavailable or unresponsive, it’ll try the next one in line, based on the order of priority.
Getting your MX records right is crucial not only for email to function properly but also for your domain’s security. A wrong MX setup can cause delivery failures and open the door to spam, phishing, or other malicious behavior.
Common MX Misconfigurations
Despite their importance, MX records are often misconfigured, and that can lead to serious consequences. Here are some of the most common mistakes:
- Missing MX record: If your domain doesn’t have an MX record, mail servers won’t be able to find a destination for the emails they’re trying to send you. The result? You simply won’t receive any emails.
- Incorrect priority settings: As we mentioned earlier, MX records come with priority levels. If these priorities aren’t set up correctly, especially when you have multiple MX records, it can lead to delayed delivery, failed deliveries, or email being routed in the wrong order.
- Pointing to a wrong or non-existent server: If your MX record is directing emails to an incorrect or non-existent server, you’ll lose incoming messages. Worse yet, those emails might end up on an unauthorized or unknown server.
- Using outdated or insecure servers: Relying on mail servers that are no longer supported or that aren’t secure is a bad idea. It creates vulnerabilities and could allow unauthorized access to the sensitive information your emails might contain.
- Pointing to open relay servers: If your MX record points to a mail server that’s configured as an open relay, your domain could be hijacked for sending spam. That hurts your reputation and could get you blacklisted.
Security Risks
Having poorly configured MX records can seriously undermine your domain’s integrity and expose you to various security misconfigurations and threats. Some of the most common risks include:
- Failed email delivery: MX misconfigurations can lead to errors or bounces when someone tries to send you a message. That disrupts communication and could result in lost opportunities or important emails never reaching you.
- Phishing and spoofing attacks: Attackers often exploit MX misconfigurations, especially when your domain lacks proper authentication measures like SPF, DKIM, and DMARC. This makes it much easier for them to send emails that appear to come from your domain, tricking recipients into handing over sensitive data. In some cases, they may even use phishing subdomains that closely mimic your domain name to increase their chances of success.
- Malware and spam distribution: If your MX records point to an open relay server, spammers can abuse your domain to send unsolicited emails or even distribute malware, using your domain as a disguise.
- Man-in-the-middle (MITM) attacks: If your MX records direct email traffic through compromised or untrusted servers, attackers could intercept and read your messages, steal information, or inject malicious content before it reaches its destination.
How Attackers Exploit MX Misconfigurations
Cybercriminals are always on the lookout for MX misconfigurations that they can exploit. Some of the most common tactics include:
- Email spoofing: A bad MX configuration combined with weak email authentication (like missing SPF records) makes it easy for attackers to send fraudulent emails that appear to come from your domain. This is often used in phishing or spam campaigns and can lead to data breaches or financial losses, not to mention damage to your brand.
- Hijacking email traffic: If your MX records point to outdated or incorrect servers, a malicious actor could redirect that traffic to their own mail server. This gives them access to sensitive information and breaks the chain of trust between senders and recipients.
- Spam campaigns: Another common scenario is attackers using your misconfigured domain for spam campaigns. Once that happens, your domain could be flagged, blocked, or blacklisted, even if you didn’t send the spam yourself.
How to Detect MX Misconfigurations
The most effective way to identify problems with your MX configuration is by using a specialized tool, like our web security scanner. This online tool can analyze several aspects of your domain’s security, including your MX records.
To use it, just click the link in the paragraph above to access the tool. Then, enter your domain name into the input field and click the Scan button to begin the security check.
In just a few seconds, you’ll get a report showing whether your MX records are correctly set up or if there’s anything you need to fix.
Best Security Practices
Avoiding MX misconfigurations helps protect your domain and maintain the trust of your users and customers. Here are some best practices you should follow:
Double-check the syntax of your records. Start by getting the correct MX records from your email provider, then make sure they’re set up properly, with no typos, correct hostnames, and properly configured priorities.
Avoid open relay servers; these types of servers are often used by spammers and have a bad reputation. If your MX record points to an open relay, your domain could be abused for malicious activity.
Implement SPF, DKIM, and DMARC; these DNS records add a layer of authentication to your outgoing emails, helping to prevent spoofing and ensuring that your messages come from verified sources.
Monitor and audit your MX records regularly to check for unauthorized changes, especially after updates or migrations. Likewise, keep your email server software up to date and use the latest stable versions to avoid vulnerabilities, particularly those listed in CVEs affecting DNS servers, which can be exploited to manipulate or poison DNS records, including MX entries
Summary
MX misconfigurations are more common and more dangerous than many people realize. They can cause email delivery issues, security risks, and open the door to phishing, spoofing, or spam attacks.
The key to avoiding them is using the right tools, setting up records carefully, and monitoring your domain regularly. Don’t wait for a breach to realize that your MX records are broken.